1. Field of the Invention
The invention relates to a process for producing tiles, particularly to a process for producing tiles from waste material including industrial and household wastes.
2. Description of the Related Art
It is known in the art to produce tiles and building blocks from trash and a binding composition composed of magnesium oxide, magnesium chloride and a modifying agent. The modifying agent is used to reduce excess magnesium ions which can result in moisture absorption in the final products, and includes ferrous sulfate, copper sulfate, magnesium sulfate, potassium permanganate, urea-formaldehyde resin and ammonium chloride. A conventional process for producing tiles includes the steps of adding an amount of magnesium chloride into an amount of water to form an aqueous solution of magnesium chloride, adding an amount of the modifying agent and an amount of magnesium oxide into the aqueous solution of magnesium chloride, stirring homogeneously to form the binding composition, mixing the binding composition with the waste material, which is pre-treated, and molding the resulting mixture into tiles. Although the aforesaid process can produce tiles from waste material to achieve the purpose of waste recycling, the tile produced thereby has the following shortcomings:
1. Since the effect of the modifying agent is insufficient, the excess magnesium ions remaining in the tiles can result in moisture absorption which can reduce toughness and produce cracks.
2. Since the modifying agent is devoid of an ingredient to degrade heavy metal toxic substances in the waste material, the toxic substances remaining in the tiles are liable to degrade in use and tend to release foul and/or toxic gases which are harmful to the environment.
In the process of the prior art, the binding composition consisting of magnesium chloride, water, magnesium oxide and the modifying agent is produced first, and is subsequently added to the pre-treated waste material. It is difficult to mix the waste material with the individual ingredients constituting the binding composition homogeneously, which would in turn adversely affect the effect of the binding composition to bind the waste material, thereby reducing the toughness of the tiles.
Therefore, the object of the present invention is to provide a process for making tiles, which can solve the problems encountered in the prior art, such as moisture absorption, susceptibility to cracking, reduced toughness, and the release of foul and/or harmful gases.
According to this invention, a process for producing tiles comprises the steps of:
(1) grinding waste material to a reduced size;
(2) removing ferrous metals from the waste material; and
(3) mixing the waste material with a binder to form a mixture after grinding, and molding the mixture,
wherein the binder comprises:
magnesium oxide;
a regulating agent for accelerating the hardening of the magnesium oxide;
a modifying agent selected from the group consisting a water-reducing agent, a water-repellent agent, a water-resistant enhancing agent, and an active agent which can react with excess magnesium ions in the binder to form an insoluble magnesium salt; and
a degrading agent for degrading heavy metal toxic substances contained in the waste material.
The process of this invention contemplates recycling waste material, such as those containing organic and inorganic substances. The waste material includes industrial wastes and household wastes. The household wastes may contain kitchen waste, vegetable and fruit residue, paper, plastics, wood segments, fibers, glass, metals, etc.
In the process according to the present invention, the waste material is subjected to grinding, preferably followed by a sieving step so as to reduce the size of the waste material. Ferrous metal substances are preferably removed from the waste material via a magnetic selector.
Magnesium oxide is a main binder component used in the present invention. The regulating agent is used to assist in hardening of the magnesium oxide, and is preferably selected from the group consisting of magnesium chloride, magnesium sulfate, and ferrous sulfate.
The modifying agent used in the process of the present invention may be selected from the group consisting of: a water-reducing agent such as naphthyl sulfonate; a water-repellent agent such as inorganic ferric salt (for example, ferric chloride and ferrous sulfate) and inorganic aluminum salt; a water-resistant enhancing agent such as a water-soluble or water-emulsifiable polymer selected from the group consisting of styrene-methyl acrylate copolymer, polymethyl acrylate, polyvinylidene chloride, ethyl silicate and butyl benzene; and an active agent which can react with excess magnesium ions to form an insoluble magnesium salt. Preferably, the active agent is selected from the group consisting of pumice, ashrock, phosphate, copper sulfate and hydrochloric acid.
In order to remove heavy metal toxic substances from the waste material and to prevent the tiles produced by the present invention from releasing toxic substances and unpleasant odor, the degrading agent is used in the process for the purposes of reducing or eliminating toxicity of the heavy metal toxic substances contained in the waste material. The degrading agent usable in the present invention includes at least one compound selected from the group of consisting of vitamin, such as vitamin B12 and vitamin C, tetrahydrofolid acid, and a chelating agent, such as ethylenediamine tetracetic acid.
The regulating agent and the modifying agent used in the process of the present invention must be of a suitable amount so as to prevent the final products produced thereby from absorbing moisture. In a preferred embodiment of the present invention, based on 100% by weight of the mixture of the waste material and the binder, the amount of the waste material is 60% to 80%, the amount of the magnesium oxide is 19-25%, the amount of the regulating agent is 11.7-13%, the amount of the modifying agent is 1.04-1.60%, and the amount of the degrading agent is 0.26 to 0.40%.